Concerns with global warming and dwindling fossil fuel reserves have motivated research into the development of effective catalysts for converting CO2, a prominent waste compound, into value added chemical feedstocks and fuels. Recent works have demonstrated that metal nanostructures, particularly those composed of Au and Cu, are catalysts for CO2 reduction under both electrochemical bias and plasmonic excitation. However, these materials are known to dynamically evolve in reactive environments; for instance, binding of adsorbates drive reshaping and redox reactions can have dramatic effects on material properties, e.g., evolution from a metallic to an oxide surface. Such processes can dramatically alter catalytic efficacy and behaviors of these materials. Thus, understanding these dynamics as they occur on the nanoscale will aid in the design and engineering of novel catalyst materials. In-situ transmission electron microscopy is a powerful tool for such studies. Using the dynamic environmental TEM (DETEM) developed at the University of Illinois, the evolution of oxidized Cu nanoparticles under plasmonic excitation was studied. It was found that under these conditions, the nanoparticles transform from core–shell to hollow shell structures. This hollowing process was followed with high spatiotemporal resolution revealing the nucleation of voids and following their growth. For the majority of hollowing nanoparticles (61 out of 65), one void nucleus was observed, but in several (4 out of 65) two void nuclei were observed. Further, we identified the prominent crystallographic directions along which voids grows. The role of plasmonic excitation was to enhance the rate of void nucleation resulting in faster hollowing. Additionally, plasmon-assisted hollowing appears to follow a different pathway from hollowing induced by steady-state heating, which is likely due to differences in the nanoscale heating profile. Our studies showcase the capabilities of the DETEM for probing the dynamics of evolution of nanomaterials in operando.

In-situ electron microscopy of plasmon-assisted transformations of Cu nanoparticles

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ACS Fall 2022

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